1. Field of the Invention
This invention relates to measuring tools, and in particular, to a three-dimensional measuring device for use on a machine tool having a numerical position readout.
2. Description of the Prior Art
The fabrication of large turbogenerator apparatus requires precise machining and dimensioning or else faulty manufacture may result in premature failure of the apparatus. Presently, the measurement of each dimension for members fabricated for use in large dynamoelectric apparatus is done by using a separate measuring device for each measurement that is required to be taken. Each measurement device, whether micrometer, pin gauge, or journal, which must be used in the measurement process is calibrated in a meter room and brought to the work floor to the stock on which machining is being performed, and the measurement is then taken.
The various gauges, in addition to being difficult to calibrate, are each possibly subject to varying degrees of accuracy due to varying responses to temperature and humidity conditions. In addition, some devices are cumbersome to use and may require more than one man to operate. Often, such gauges rely upon an operator's "touch" rather than more objective criteria. As an example, measurements on the order of 20-25 feet, with permissible tolerances of thousandths of an inch, such as those taken for bore of a large dynamoelectric apparatus unit, are usually accomplished by two men using a pin gauge that is precisely measured by electronic techniques in the meter room.
The pin gauge is an elongated metal rod that, for purposes of the measurement, is held in place by one workman against one point on the stock being machined. The second end of the gauge is then swung by the second workman in short acrs using the first workman's pivot point as center of the arc. The degree of abrasion between the second end of the pin gauge and the stock opposite the pivot point indicates to a skilled workman the overage that must be trimmed in order to meet the prescribed dimension.
Of course, it is plain that such a pin gauge is affected by temperature and humidity conditions which might change its dimension slightly from the meter room to the work floor. But more importantly, the gauge is cumbersome to use and relies upon the "feel" of the workman, and not upon some more objective standard.
When measuring more than one dimension, it is required that a separate gauge for each dimension be brought from the meter room to the work floor and the measurements taken of the stock being machined. In addition to the variations induced in each gauge by the change in temperature and humidity conditions from the meter room to the work floor, the time involved in taking separate measurements, some measurements involving two workmen, is expensive. It is apparent therefore that a more accurate and expeditious measuring device able to measure the dimension of machined stock on each of three orthogonal dimensions is required.